1. Technical Field
The present disclosure relates to a mounting substrate and an electronic device and, more particularly, a mounting substrate and an electronic device having a dam to suppress a flow of an underfill material.
2. Background Art
Recently, as the method of mounting an electronic element such as a semiconductor chip on a mounting substrate, flip-chip mounting is used frequently. The flip-chip mounting is such a method that bumps are formed on a mounting surface of the electronic element and then the electronic element is face-down bonded to electrodes formed on the mounting substrate.
In this flip-chip mounting, the electronic element and the mounting substrate are bonded by bonding force between the bumps and the electrodes. Thus, once a stress is generated between the electronic element and the mounting substrate, this stress is applied wholly to bonded positions between the bumps and the electrodes. Therefore, in this flip-chip mounting, normally an underfill resin (an epoxy resin is often used) is filled between the electronic element and the mounting substrate to attain the stress relaxation.
Meanwhile, a higher packaging density is desired in the electronic device such as the semiconductor device, or the like. As the package that meets this higher packaging density, much attention is focused on the system in package (SiP). Various structures have been proposed as this SiP. As one type of such structures, there is the package on package (PoP) that realizes the SiP structure by stacking the package (semiconductor device) in which a single semiconductor chip is packaged and the package in which a plurality of semiconductor chips are stacked.
In the case of SiP having this PoP structure, normally the package serving as the lower layer and the package serving as the upper layer are bonded mutually using the solder balls. Therefore, in the package serving as the lower layer, the electrodes that are bonded to the solder balls must be formed on an upper surface of the mounting substrate on which the semiconductor chip is mounted. That is, both the chip mounting area on which the semiconductor chip is mounted and the electrode forming area in which the electrodes are formed are formed on the upper surface of the mounting substrate constituting the package serving as the lower layer. Since usually the electrodes are arranged to surround the semiconductor chip, the electrode forming area is arranged to surround the chip mounting area.
Here, when the package serving as the lower layer has such a structure that the semiconductor chip is flip-chip mounted, the underfill resin must be filled between the semiconductor chip and the mounting substrate to attain the stress relaxation, as described above. However, since the underfill resin has a flowability during the filling operation, it is feared that such underfill resin flows out from the chip mounting area into the electrode forming area.
For this reason, the dam member for blocking flow out of the underfill resin from the chip mounting area into the electrode forming area is provided between the chip mounting area and the electrode forming area in the related-art (see e.g., Japanese Unexamined Patent Publication: JP-A-2005-276879).
FIGS. 4A and 4B show an example of a mounting substrate having the dam member in the related-art. FIG. 4A is a view showing a forming position and its neighborhood of a dam member 105 of a mounting substrate 100 in an enlarged fashion, and FIG. 4B is a sectional view of the same.
A dam member 105 is formed between an electrode forming area 103 in which electrodes 101 are formed and a chip mounting area 102 on which a semiconductor chip (not shown) is mounted, as described above. In the electrode forming area 103, the electrodes 101 are exposed from the openings formed in a solder resist 104. Also, the underfill resin is filled in the chip mounting area 102 after the semiconductor chip is mounted.
According to the related-art, the dam member 105 is formed like a frame shape. Also, the dam member 105 and the electrodes 101 are arranged relatively distantly in the past when the requested packaging density is not so higher than the recent year.
However, there is a tendency recently that the semiconductor chip is increasing in size according to its greater functionality, and thus the number of terminals tends to increase. In contrast, as to the mounting substrate on which the semiconductor chip is mounted, a smaller area is desired to meet a demand for size reduction of the electronic device that is mounted on the mounting substrate.
Therefore, with respect to the chip mounting area 102 and the electrode forming area 103 formed on the mounting substrate, the chip mounting area 102 must be increased in area in response to an increase of size of the semiconductor chip, and also the electrode forming area 103 must be increased in area in response to an increase of the number of electrodes. In addition, the mounting substrate 100 must be reduced in area as a whole, as described above.
In the related-art, such a problem existed that this mounting substrate 100 cannot meet respective requests at the same time. Also, as the means for fulfilling these requests, it may be considered that a width of the dam member 105 should be narrowed. However, when a width of the dam member 105 is narrowed, a bonded area of the dam member 105 to a substrate body 100a is narrowed and correspondingly a mechanical strength is lowered. As a result, the dam member 105 is damaged in filling the underfill resin, and thus it is feared that flow out of the underfill resin into the electrode forming area 103 cannot be prevented effectively.